Goodwill and Intangible Assets (Narrative) (Details)	12 Months Ended
Goodwill and Intangible Assets (Narrative) (Details)	Dec. 31, 2016 division segment
Segment Reporting Information [Line Items]
Number of reportable segments	5
NBCUniversal Media LLC [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	4
Cable Communications [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
Cable Communications [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Number of divisions \| division	3
Software [Member]
Segment Reporting Information [Line Items]
Finite-lived intangible asset amortization period	4 years
Software [Member] \| Maximum [Member]
Segment Reporting Information [Line Items]
Finite-lived intangible asset amortization period	5 years
Software [Member] \| NBCUniversal Media LLC [Member]
Segment Reporting Information [Line Items]
Finite-lived intangible asset amortization period	5 years
Software [Member] \| NBCUniversal Media LLC [Member] \| Maximum [Member]
Segment Reporting Information [Line Items]
Finite-lived intangible asset amortization period	5 years